The long term goal of the proposed research is to use biochemical and cell biological approaches including morphological (transmission electron microscopy, scanning electron microscopy, autoradiography, X-ray microprobe analysis, fluorescent antibody studies, fluorescent photobleach) and cell fractionation techniques to analyze structurally and functionally the integrative mechanism by which hormones regulate adipocyte metabolism. In particular, emphasis will be placed on understanding the mechanism of insulin action. The key areas to be studied will include: a. Insulin-receptor interactions using 125I-insulin, monomeric ferritin-insulin, monomeric ferritin-125I-insulin and monomeric 125I-ferritin-insulin to study hormone binding and degradation and their relationships to biological activities. In addition these agents will be used to study the fate of the insulin receptor and the possible internalization of insulin or pieces of it. b. Insulin-induced membrane responses, including alterations in membrane phosphorylation reactions, cytochalasin B binding and glucose transport by direct addition of insulin to the membranes. C. Insulin-induced alterations in calcium subcellular distribution. This requires treatment of intact cells with insulin prior to fractionation. The importance of the endoplasmic reticulum in regulating intracellular cytosol calcium will be emphasized.